Effects Of Conservation Tillage On Ecological Stoichiometric Characteristics And Microbial Diversity Of Farmland Black Soil

Northeast black soil area is an important grain production area in China,black soil is known for high organic matter content,fertile soil,mostly distributed in Manchuan Mangang,gentle slope,large catchment area and other areas,but in recent years soil erosion phenomenon is very common,nutrient loss is serious,productivity is affected.The frequent use of tilling and tillage measures has led to the long-term overload utilization of farmland black soil,and the soil fertility has decreased year by year,which has aggravated soil erosion and seriously affected the quality and grain yield performance of black soil cultivated land.Therefore,the effects of conservation tillage on the ecological stoichiometry characteristics and microbial diversity of soil,extracellular enzymes and microbial biomass C,N and P were studied,and the relationship between conservation tillage and soil nutrient dynamic balance in black soil area was clarified,which provided theoretical basis and technical support for stabilizing the function and soil fertility improvement of black soil ecosystem.This study takes the farmland black soil experimental field as the object.The experiment started in 2019.The settings include tillage（DR）,rotary tillage（RR）,conventional no-tillage（NR）,no-tillage and straw-covering（CR）,and no-tillage and straw-covering+intertillage（C₁R）5 kinds of farming methods,continuously analyze soil nutrients（C,N,P）,enzyme activity,microbial biomass,etc.in 2020～2021,in order to explore the ecological stoichiometric characteristics of soil C,N,P in traditional farming and conservation According to the law of change under permanent tillage,explore suitable black soil protective tillage methods in this area,so as to alleviate or improve soil degradation.The research conclusions are as follows:（1）Different tillage methods had significant effects on soil mechanical composition.In 2020,the proportion of very fine sand and fine sand in the 0～15cm soil layer was higher than that of15～30cm,and the content of clay and silt was lower than that of 15～30cm.In 2021,the proportion of clay,silt and very fine sand in 0～15cm soil layer was higher than 15～30cm,and the proportion of fine sand was lower than 15～30cm.Compared with traditional tillage（DR,RR）,conservation tillage（NR,CR,C₁R）significantly increased the content of silt and clay,but decreased the content of median particle size（D50）and corrosion-prone particles.（2）The contents of soil organic carbon（SOC）,total nitrogen（TN）and total phosphorus（TP）under conservation tillage treatment were significantly higher than those under traditional tillage treatment,and the effect of avoiding tillage with straw was the best,and increased with the increase of treatment years.The highest SOC,TN and TP contents in surface soil were 1.74 g·kg^-1,1.85 g·kg^-1 and 0.46 g·kg^-1,respectively.The nutrient content in surface soil was higher than that in deep soil.In the 0～15cm soil layer,soil C/N under traditional tillage was higher than that under conservation tillage,but the result was opposite in the 15～30cm soil layer.Soil C/P and N/P in 0～30cm soil layer showed a trend that conservation tillage treatment was higher than traditional tillage treatment.In conclusion,conservation tillage treatment is beneficial to the improvement of soil nutrients and the cyclic transformation between nutrients.（3）The activities ofβ-D-glucosidase（βG）,N-1,4-acetylglucosidase（NAG）,leucine aminopeptidase（LAP）and acid phosphatase（ACP）in 2021 were higher than those in 2020.Tillage had significant effects on soil enzyme activities.Compared with traditional tillage treatment,conservation tillage treatment had different degrees of improvement in enzyme activities,and no-tillage treatment with straw cover had the best improvement effect.In 0～15cm soil layer,ln（βG）:ln（NAG+LAP）,ln（βG）:ln（ACP）and ln（NAG+LAP）:ln（ACP）showed that conservation tillage was better than traditional tillage,and the effect of avoiding tillage and intertilling was the best.ln（βG）:ln（NAG+LAP）and ln（βG）:ln（ACP）were significantly higher than those of other treatments in the 15～30cm soil layer.The vector Angle of soil enzyme activity under all tillage methods was less than 45?.The vector length of soil enzymes under different tillage methods ranged from 1.19 to 1.35,while the vector length of soil enzymes under no-tillage mulching and medium-tillage treatment increased significantly in 2021.（4）Conservation tillage significantly increased the contents of soil microbial biomass carbon,microbial biomass nitrogen and microbial biomass phosphorus.In 2020,the soil microbial biomass carbon and nitrogen contents in the 0～30cm soil layer were the highest in the no-tillage+medium tillage treatment,and the microbial biomass phosphorus content in the 0～15cm soil layer was the highest in the traditional no-tillage treatment,which was 24.90 mg·kg^-1,and 11.75 mg·kg^-1 in the15～30cm soil layer.In 2021,the contents of carbon,nitrogen and phosphorus of soil microbial biomass in 0～30cm soil layer were the highest under no-tillage and stover treatment.In 2020,MBC/MBN in 0～30cm soil layer was the highest under no-tillage mulch treatment,and MBC/MBP and MBN/MBP in no-tillage mulch+medium tillage treatment were significantly higher than other treatments.In 2021,MBC/MBN under no-tillage mulch treatment was significantly higher than that under other treatments.MBC/MBP under traditional no-tillage treatment was the highest,MBN/MBP under deep-turning treatment was the highest in 0～15cm soil layer,and MBN/MBP under traditional no-tillage treatment was the highest in 15～30cm soil layer.（5）Conservation tillage treatment significantly increased the ACE and chao indices of bacteria and fungi,and no-tillage mulching treatment had the most significant effect on bacterial diversity.On the bacterial level,conservation tillage significantly increased Chloroflexi,Actinobacteriota,Proteobacteria,Acidobacteriota and Chloroflexi.The relative abundance of Gemmatimonadota and Myxococcota significantly decreased Firmicutes,Bacteroidota,Verrucomicrobiota.The relative abundance of the phylum Planctomycetota,Methylomirabilota.At the fungal level,compared with traditional tillage,conservation tillage significantly increased the relative abundance of Ascomycota,Basidiomycota and Chytridiomycota,while significantly decreased the relative abundance of Mortierella omycota.In conclusion,conservation tillage measures had significant effects on the ecological stoichiometry characteristics and microbial diversity of soil,extracellular enzymes and microbial masses C,N and P in the experimental area,which could improve soil structure,increase soil nutrients,and coordinate water,fertilizer,gas and heat.